Identification of a Rotating Sound Source in a Duct with High Spatial Resolution

Invited paper

Jeong-Guon Ih


Wednesday 3 june, 2015, 14:40 - 15:00

0.3 Copenhagen (49)

Spatial distribution of acoustic parameters at the source plane provides important information for development or refinement of quiet in-duct fluid machines. Inverse estimation techniques using measured in-duct pressures and sound propagation models can be used for source identification. However, when the acoustic source is rotating, it is not easy to identify the source parameter distribution clearly in source planes of complicated shapes. In this work, a method is suggested for identifying rotating noise sources in a duct with a reasonable spatial resolution. For obtaining detailed information about the source distribution, evanescent waves are included in the propagation model based on the modal summation method. The Doppler effect caused by source rotation is also considered in the modeling. For validating the suggested method, an experiment is conducted in a duct system with a rotating loudspeaker, which radiates a pure tone, in the absence of flow. The measured near-field pressure shows the shift of spectral peaks due to the Doppler effect. The modal amplitudes related to the rotation of loudspeaker are estimated to obtain the source parameters. The near-field sound pressure is regenerated from the estimated modal amplitudes, giving a maximum error less than -10 dB. The pressure and velocity fields over the source plane are calculated using the estimated modal amplitudes. The reconstructed result clearly indicates the rotating loudspeaker as the main noise source in the rotating reference frame.

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